69 
1906-7.] Functions of the Rolandic Cortex in Monkeys. 
Beevor and Horsley * * * § extended their investigations to the brain of the 
anthropoid. They came to the conclusion that the excitable area in the 
cortex of the orang-utan — the animal employed by them — was less in 
extent than had been believed to be the case in the lower ape, and that it 
was much interrupted by spaces from which no effect could be obtained 
even by the application of strong stimuli. The upper third of the ascend- 
ing parietal convolution, and the part of the paracentral lobule behind a 
continuation over the margin of the upper end of the Rolandic fissure, they 
found entirely or almost entirely inexcitahle. The lower portion of the 
ascending parietal convolution they considered to form part of the motor 
area. In the frontal lobe the only excitable area found by them lay 
immediately in front of the precentral sulcus, and its stimulation caused 
turning of the eyes to the opposite side. 
Grlinbaum and Sherrington j- investigated the cerebral cortex in the 
orang, gorilla, and two species of chimpanzee ( Troglodytes niger and 
Troglodytes calvus). The method adopted was that which Sherrington had 
used l in his work on the cortex of the lower apes, viz., unipolar faradisa- 
tion. These observers found in these animals that the motor area is 
continuous, that it embraces the whole length of the ascending frontal 
convolution, extending above over the margin to include part of the mesial 
surface of the hemisphere, stopping short, however, of the calloso-marginal 
fissure, and that its posterior boundary lies within the Rolandic fissure. 
In no case did the motor area extend into the ascending parietal convolu- 
tion, although occasionally the posterior wall of the fissure of Rolando was 
found to he excitable. It was found impossible to obtain muscular move- 
ments by stimulation of the ascending parietal convolution when the 
ascending frontal convolution had been destroyed. § 
Within the motor area it was found possible to localise, among others, 
movements of the nostril, palate, chest wall, anal and vaginal orifices. 
Inhibition effects were also obtained. The anterior boundary of the motor 
area could not be represented as a definite sharp line, but the excitable area 
was found to fade off gradually in an anterior direction. Conjugate devia- 
tion of the eyeballs was caused by stimulation of a region in the frontal lobe 
separated from the Rolandic motor area by a field of inexcitahle cortex. 
The reactions of this region differed markedly from those of the Rolandic 
motor cortex, and it was placed by the authors in a different category. 
* Phil. Trans., 1890. 
t Proc. Roy. Soc., London, 1901, vol. lxix. p. 206. 
X Ibid., 1893, vol. lii. 
§ Ibid., 1903, vol. lxxii. p. 152. 
